New natural furfural derivatives from the leaves and stems of Pogostemon cablin
A new furfural derivative, pogoscafuran A (1), a new natural product, HMF levulinate (2), together with four known compounds (3–6) were isolated from an extract of the leaves and stems of Pogostemon cablin (Blanco) Benth. Their structures were elucidated on the basis of extensive spectroscopic analyses and single-crystal X-ray crystallography. Compound 1 was the first example of natural furfural derivative with a unique C5–C1′ linkage between a molecule of furfural and 3-methyl-2-cyclopentenone moiety. The plausible biogenetic pathway for the new compound 1 was proposed. All these isolated compounds were tested for their inhibitory effects on the nitric oxide (NO) production induced by lipopolysaccharide in RAW264.7 cells, and only compound 1 exhibited weak inhibitory activity.